But, what about goals like
?- plus(X,2,6). ?- plus(2,Y,7).or even
?- plus(X,Y,5).
The interpreter will generate: X = 4 for first query, and Y = 5 for second query, and many answers for the third query including
<X = 1, Y = 4>, <X = 2, Y = 3>, ...Question: What about a goal like plus(X,Y,Z)?